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   <p data-fill-with="logo"><a class="logo" href="https://www.w3.org/"> <img alt="W3C" height="48" src="https://www.w3.org/StyleSheets/TR/2016/logos/W3C" width="72"> </a> </p>
   <h1 class="p-name no-ref" id="title">CSS Rhythmic Sizing</h1>
   <h2 class="no-num no-toc no-ref heading settled" id="subtitle"><span class="content">Editor’s Draft, <time class="dt-updated" datetime="1970-01-01">1 January 1970</time></span></h2>
   <details>
    <summary>Specification Metadata</summary>
    <div data-fill-with="spec-metadata">
     <dl>
      <dt>This version:
      <dd><a class="u-url" href="https://drafts.csswg.org/css-rhythm/">https://drafts.csswg.org/css-rhythm/</a>
      <dt>Latest published version:
      <dd><a href="https://www.w3.org/TR/css-rhythm-1/">https://www.w3.org/TR/css-rhythm-1/</a>
      <dt>Test Suite:
      <dd><a href="http://test.csswg.org/suites/css-rhythm-1_dev/nightly-unstable/">http://test.csswg.org/suites/css-rhythm-1_dev/nightly-unstable/</a>
      <dt class="editor">Editors:
      <dd class="editor p-author h-card vcard" data-editor-id="45369"><a class="p-name fn u-email email" href="mailto:kojiishi@gmail.com">Koji Ishii</a> (<span class="p-org org">Google</span>)
      <dd class="editor p-author h-card vcard" data-editor-id="35400"><a class="p-name fn u-url url" href="http://fantasai.inkedblade.net/contact">Elika J. Etemad / fantasai</a> (<span class="p-org org">Invited Expert</span>)
      <dt>Suggest an Edit for this Spec:
      <dd><a href="https://github.com/w3c/csswg-drafts/blob/master/css-rhythm-1/Overview.bs">GitHub Editor</a>
      <dt>Issue Tracking:
      <dd><a href="https://github.com/w3c/csswg-drafts/labels/css-rhythm-1">GitHub Issues</a>
     </dl>
    </div>
   </details>
   <div data-fill-with="warning"></div>
   <p class="copyright" data-fill-with="copyright"><a href="https://www.w3.org/Consortium/Legal/ipr-notice#Copyright">Copyright</a> © 1970 <a href="https://www.w3.org/"><abbr title="World Wide Web Consortium">W3C</abbr></a><sup>®</sup> (<a href="https://www.csail.mit.edu/"><abbr title="Massachusetts Institute of Technology">MIT</abbr></a>, <a href="https://www.ercim.eu/"><abbr title="European Research Consortium for Informatics and Mathematics">ERCIM</abbr></a>, <a href="https://www.keio.ac.jp/">Keio</a>, <a href="https://ev.buaa.edu.cn/">Beihang</a>). W3C <a href="https://www.w3.org/Consortium/Legal/ipr-notice#Legal_Disclaimer">liability</a>, <a href="https://www.w3.org/Consortium/Legal/ipr-notice#W3C_Trademarks">trademark</a> and <a href="https://www.w3.org/Consortium/Legal/2015/copyright-software-and-document">permissive document license</a> rules apply. </p>
   <hr title="Separator for header">
  </div>
  <div class="p-summary" data-fill-with="abstract">
   <h2 class="no-num no-toc no-ref heading settled" id="abstract"><span class="content">Abstract</span></h2>
   <p>This module contains CSS features for aligning content size

  to multiple of unit size.</p>
    <a href="https://www.w3.org/TR/CSS/">CSS</a> is a language for describing the rendering of structured documents
(such as HTML and XML)
on screen, on paper, etc. 
  </div>
  <h2 class="no-num no-toc no-ref heading settled" id="status"><span class="content">Status of this document</span></h2>
  <div data-fill-with="status">
   <p> This is a public copy of the editors’ draft.
	It is provided for discussion only and may change at any moment.
	Its publication here does not imply endorsement of its contents by W3C.
	Don’t cite this document other than as work in progress. </p>
   <p> <a href="https://github.com/w3c/csswg-drafts/issues">GitHub Issues</a> are preferred for discussion of this specification.
	When filing an issue, please put the text “css-rhythm” in the title,
	preferably like this:
	“[css-rhythm] <i data-lt>…summary of comment…</i>”.
	All issues and comments are <a href="https://lists.w3.org/Archives/Public/public-css-archive/">archived</a>,
	and there is also a <a href="https://lists.w3.org/Archives/Public/www-style/">historical archive</a>. </p>
   <p> This document was produced by the <a href="https://www.w3.org/Style/CSS/">CSS Working Group</a>. </p>
   <p> This document was produced by a group operating under
	the <a href="https://www.w3.org/Consortium/Patent-Policy/">W3C Patent Policy</a>.
	W3C maintains a <a href="https://www.w3.org/2004/01/pp-impl/32061/status" rel="disclosure">public list of any patent disclosures</a> made in connection with the deliverables of the group;
	that page also includes instructions for disclosing a patent.
	An individual who has actual knowledge of a patent which the individual believes contains <a href="https://www.w3.org/Consortium/Patent-Policy/#def-essential">Essential Claim(s)</a> must disclose the information in accordance with <a href="https://www.w3.org/Consortium/Patent-Policy/#sec-Disclosure">section 6 of the W3C Patent Policy</a>. </p>
   <p> This document is governed by the <a href="https://www.w3.org/2019/Process-20190301/" id="w3c_process_revision">1 March 2019 W3C Process Document</a>. </p>
   <p></p>
  </div>
  <div data-fill-with="at-risk"></div>
  <nav data-fill-with="table-of-contents" id="toc">
   <h2 class="no-num no-toc no-ref" id="contents">Table of Contents</h2>
   <ol class="toc" role="directory">
    <li>
     <a href="#intro"><span class="secno">1</span> <span class="content">Introduction</span></a>
     <ol class="toc">
      <li><a href="#eastasia"><span class="secno">1.1</span> <span class="content">East Asian Casual Vertical Rhythms</span></a>
     </ol>
    <li>
     <a href="#block-height"><span class="secno">2</span> <span class="content">Adjusting Block-level Box Heights</span></a>
     <ol class="toc">
      <li><a href="#block-step-size"><span class="secno">2.1</span> <span class="content">Specifying the Step Size: the <span class="property">block-step-size</span> property</span></a>
      <li><a href="#block-step-insert"><span class="secno">2.2</span> <span class="content">Specifying the Spacing Type: the <span class="property">block-step-insert</span> property</span></a>
      <li><a href="#block-step-align"><span class="secno">2.3</span> <span class="content">Specifying Alignment: the <span class="property">block-step-align</span> property</span></a>
      <li><a href="#block-step-round"><span class="secno">2.4</span> <span class="content">Rounding Method: the <span class="property">block-step-round</span> property</span></a>
      <li><a href="#block-step"><span class="secno">2.5</span> <span class="content">Block Step Adjustment Shorthand: the <span class="property">block-step</span> shorthand</span></a>
     </ol>
    <li><a href="#line-height-step"><span class="secno">3</span> <span class="content">Adjusting Line Box Heights: the <span class="property">line-height-step</span> property</span></a>
    <li><a href="#priv-sec"><span class="secno">4</span> <span class="content">Privacy and Security Considerations</span></a>
    <li><a href="#acks"><span class="secno">5</span> <span class="content">Acknowledgments</span></a>
    <li>
     <a href="#conformance"><span class="secno"></span> <span class="content"> Conformance</span></a>
     <ol class="toc">
      <li><a href="#document-conventions"><span class="secno"></span> <span class="content"> Document conventions</span></a>
      <li><a href="#conform-classes"><span class="secno"></span> <span class="content"> Conformance classes</span></a>
      <li>
       <a href="#conform-responsible"><span class="secno"></span> <span class="content"> Requirements for Responsible Implementation of CSS</span></a>
       <ol class="toc">
        <li><a href="#conform-partial"><span class="secno"></span> <span class="content"> Partial Implementations</span></a>
        <li><a href="#conform-future-proofing"><span class="secno"></span> <span class="content"> Implementations of Unstable and Proprietary Features</span></a>
        <li><a href="#conform-testing"><span class="secno"></span> <span class="content"> Implementations of CR-level Features</span></a>
       </ol>
     </ol>
    <li>
     <a href="#index"><span class="secno"></span> <span class="content">Index</span></a>
     <ol class="toc">
      <li><a href="#index-defined-here"><span class="secno"></span> <span class="content">Terms defined by this specification</span></a>
      <li><a href="#index-defined-elsewhere"><span class="secno"></span> <span class="content">Terms defined by reference</span></a>
     </ol>
    <li>
     <a href="#references"><span class="secno"></span> <span class="content">References</span></a>
     <ol class="toc">
      <li><a href="#normative"><span class="secno"></span> <span class="content">Normative References</span></a>
      <li><a href="#informative"><span class="secno"></span> <span class="content">Informative References</span></a>
     </ol>
    <li><a href="#property-index"><span class="secno"></span> <span class="content">Property Index</span></a>
    <li><a href="#issues-index"><span class="secno"></span> <span class="content">Issues Index</span></a>
   </ol>
  </nav>
  <main>
   <h2 class="heading settled" data-level="1" id="intro"><span class="secno">1. </span><span class="content">Introduction</span><a class="self-link" href="#intro"></a></h2>
   <p>This specification provides features to control sizes of CSS objects
	according to the rules desired by use cases.</p>
   <p>Controlling sizes of CSS objects to be multiple of a unit
	is desired in many cases.
	This level of the specification focuses on following cases.</p>
   <ul>
    <li data-md>
     <p>Adjust heights of block-level boxes to multiples of the specified length.</p>
    <li data-md>
     <p>Adjust heights of line boxes to multiples of the specified length.</p>
   </ul>
   <p>By stacking blocks at multiples,
	authors can align content across columns, pages, scroll-snapped bocks
	or multiple blocks placed absolutely
	to maintain vertical rhythm.</p>
   <p>Also by controlling heights of line boxes,
	lines of text in different fonts can create consistent visuals
	to help readability.</p>
   <div class="figure">
     <a href="examples/snap-height.html"> <img src="images/snap-height-sample.png"></a> 
    <p class="caption">Vertical rhythm kept through pictures and different size of text in a multi-column document. </p>
   </div>
   <h3 class="heading settled" data-level="1.1" id="eastasia"><span class="secno">1.1. </span><span class="content">East Asian Casual Vertical Rhythms</span><a class="self-link" href="#eastasia"></a></h3>
   <p>In East Asia, a casual variant of vertical rhythm is widely used.</p>
   <p>Vertical rhythm is typically used in professional typography.
While it improves readability,
its spacing constraints require careful and well-thought design of spaces.</p>
   <p>The East Asian casual variant was
originally a product of technical constraints of traditional word processors in '80s.
But when the technical constraints were lifted in more modern technologies,
with the help of square-like visual of ideographic characters,
East Asian authors preferred to keep parts of the characteristics.</p>
   <p>In this variant of vertical rhythm,
the requirement is loosened for the ease of use for non-professional authors.
Text is still on the rhythm,
so that the majority of ideographic characters are mostly on grid,
but when author specifies borders, margins, or some other objects that may break the rhythm,
the rhythm is shifted rather than forced.
The strict vertical rhythm often surprises non-professional authors by forced jumps in such cases,
while this variant combines rhythm on text and the ease of use for non-professional authors.</p>
   <p>This variant was very widely accepted in East Asia since the middle of '90s,
such that most major word processors used in East Asia provided similar features
by default.</p>
   <p>In East Asian publishing typography,
the vertical rhythm is one of important properties,
but its priority compared to other properties
varies by types of documents.
In single column documents,
the priority is weaker than that of multi-column documents.
Text should be on the vertical rhythm,
but it is often preferred for borders, margins,
or other properties to win over the rhythm.
In such cases, the rhythm is shifted, similar to the casual variant.</p>
   <p>In this specification,
when the <a class="property" data-link-type="propdesc" href="#propdef-line-height-step" id="ref-for-propdef-line-height-step">line-height-step</a> property is used without combination of the <a class="property" data-link-type="propdesc" href="#propdef-block-step" id="ref-for-propdef-block-step">block-step</a> property
or the <a class="property" data-link-type="propdesc" href="https://drafts.csswg.org/css-line-grid-1/#propdef-line-grid" id="ref-for-propdef-line-grid">line-grid</a> property,
it produces the similar effect as the East Asian casual vertical rhythm.</p>
   <p>It may also serve good for East Asian publishing typography,
depends on the desired strength of the vertical rhythm.</p>
   <p>For other cases of vertical rhythm,
it is expected that
the <a class="property" data-link-type="propdesc" href="#propdef-block-step" id="ref-for-propdef-block-step①">block-step</a> property or the <a class="property" data-link-type="propdesc" href="https://drafts.csswg.org/css-line-grid-1/#propdef-line-grid" id="ref-for-propdef-line-grid①">line-grid</a> property are used,
or that the <a class="property" data-link-type="propdesc" href="#propdef-line-height-step" id="ref-for-propdef-line-height-step①">line-height-step</a> property is used together with them.</p>
   <h2 class="heading settled" data-level="2" id="block-height"><span class="secno">2. </span><span class="content">Adjusting Block-level Box Heights</span><a class="self-link" href="#block-height"></a></h2>
   <p>The most common typographic rhythm problems are block-level intrusions:
	when continuous paragraph-level text is interrupted
	by differently-sized content such as illustrations and headings,
	then the line-to-line rhythm can be thrown off.
	The block step properties allow such elements
	to be fitted to the rhythmic interval
	by constraining their height to a multiple of a specified step size.
	This allows content before and after the interruption
	to maintain a continuous rhythm.</p>
   <div class="figure">
     <img src="images/block-step-size-before.png" style="width: 500px"> 
    <figcaption>Heads and blockquotes have varying font sizes and line heights,
			resulting in uneven text across columns.</figcaption>
   </div>
   <div class="figure">
     <img src="images/block-step-size-after.png" style="width: 500px"> 
    <figcaption>Space inserted before and after blocks (shown with colored borders)
			restores vertical rhythm.</figcaption>
   </div>
   <p>While consistent use of the block step properties
	can produce the strictly gridded layout needed
	for parallel content flows,
	per-element specification of the step size
	also allows some interruptions to take their natural size in the flow,
	restarting the vertical rhythm afterwards.
	This can be useful in single-column layouts
	where the vertical rhythm is important to maintain visual continuity,
	but there is nothing alongside to align to.
	In these casese,
	large interruptions which visually disconnect the flow before and after
	can prioritize optimal spacing around the item
	over strict adherence to a continouous grid
	(by specifying <a class="css" data-link-type="propdesc" href="#propdef-block-step" id="ref-for-propdef-block-step②">block-step: none</a>, the initial value).</p>
   <p class="issue" id="issue-d3f7ebdb"><a class="self-link" href="#issue-d3f7ebdb"></a> This proposal can be simplified down to just the <a class="property" data-link-type="propdesc" href="#propdef-block-step-size" id="ref-for-propdef-block-step-size">block-step-size</a> property, represented solely through its shortened form as <a class="property" data-link-type="propdesc" href="#propdef-block-step" id="ref-for-propdef-block-step③">block-step</a>.
	This level will likely at most contain <span class="property" id="ref-for-propdef-block-step-size①">block-step-size</span> and <a class="property" data-link-type="propdesc" href="#propdef-block-step-insert" id="ref-for-propdef-block-step-insert">block-step-insert</a>, leaving <a class="property" data-link-type="propdesc" href="#propdef-block-step-align" id="ref-for-propdef-block-step-align">block-step-align</a> and <a class="property" data-link-type="propdesc" href="#propdef-block-step-round" id="ref-for-propdef-block-step-round">block-step-round</a> to be added if the future demands.
	The full design is described herein for current discussion and future reference.</p>
   <p class="issue" id="issue-906f23b3"><a class="self-link" href="#issue-906f23b3"></a> This proposal is currently defined to apply only to block-level boxes. This limitation is solely to simplify the first iteration; it should eventually be extended to all layout modes that honor specified heights.</p>
   <h3 class="heading settled" data-level="2.1" id="block-step-size"><span class="secno">2.1. </span><span class="content">Specifying the Step Size: the <a class="property" data-link-type="propdesc" href="#propdef-block-step-size" id="ref-for-propdef-block-step-size②">block-step-size</a> property</span><a class="self-link" href="#block-step-size"></a></h3>
   <table class="def propdef" data-link-for-hint="block-step-size">
    <tbody>
     <tr>
      <th>Name:
      <td><dfn class="dfn-paneled css" data-dfn-type="property" data-export id="propdef-block-step-size">block-step-size</dfn>
     <tr class="value">
      <th><a href="https://drafts.csswg.org/css-values/#value-defs">Value:</a>
      <td class="prod">none <a data-link-type="grammar" href="https://drafts.csswg.org/css-values-4/#comb-one" id="ref-for-comb-one">|</a> <a class="production css" data-link-type="type" href="https://drafts.csswg.org/css-values-3/#length-value" id="ref-for-length-value" title="Expands to: em | vb | ch | cm | vh | vi | in | ex | vw | ic | pt | px | lh | pc | rem | rlh | vmax | advance measure | vmin | mm | cap | q">&lt;length></a> 
     <tr>
      <th><a href="https://drafts.csswg.org/css-cascade/#initial-values">Initial:</a>
      <td>none 
     <tr>
      <th>Applies to:
      <td>block-level boxes 
     <tr>
      <th><a href="https://drafts.csswg.org/css-cascade/#inherited-property">Inherited:</a>
      <td>no 
     <tr>
      <th><a href="https://drafts.csswg.org/css-values/#percentages">Percentages:</a>
      <td>N/A 
     <tr>
      <th><a href="https://drafts.csswg.org/css-cascade/#computed">Computed value:</a>
      <td>specified keyword or absolute length 
     <tr>
      <th>Canonical order:
      <td>per grammar 
     <tr>
      <th><a href="https://drafts.csswg.org/web-animations/#animation-type">Animatable:</a>
      <td>??? 
     <tr>
      <th><a href="https://drafts.csswg.org/web-animations/#animation-type">Animation type:</a>
      <td>by computed value type 
   </table>
   <p>This property defines the <a data-link-type="dfn" href="#step-unit" id="ref-for-step-unit">step unit</a> for a block-level box’s <a data-link-type="dfn" href="https://drafts.csswg.org/css-writing-modes-4/#block-size" id="ref-for-block-size">block size</a>.
	When the <span id="ref-for-step-unit①">step unit</span> is set to a positive <a class="production css" data-link-type="type" href="https://drafts.csswg.org/css-values-3/#length-value" id="ref-for-length-value①" title="Expands to: em | vb | ch | cm | vh | vi | in | ex | vw | ic | pt | px | lh | pc | rem | rlh | vmax | advance measure | vmin | mm | cap | q">&lt;length></a>,
	the box’s outer height is rounded
	(see <a class="property" data-link-type="propdesc" href="#propdef-block-step-round" id="ref-for-propdef-block-step-round①">block-step-round</a>)
	to the closest multiple of the unit.
	Negative <span class="production" id="ref-for-length-value②" title="Expands to: em | vb | ch | cm | vh | vi | in | ex | vw | ic | pt | px | lh | pc | rem | rlh | vmax | advance measure | vmin | mm | cap | q">&lt;length></span> values are invalid.</p>
   <p>Values other than <span class="css">none</span> cause the box to <a data-link-type="dfn" href="https://drafts.csswg.org/css-display-3/#establish-an-independent-formatting-context" id="ref-for-establish-an-independent-formatting-context">establish an independent formatting context</a>.</p>
   <p>In situations where margins <a href="https://www.w3.org/TR/CSS2/box.html#collapsing-margins">collapse</a>,
	only the box’s own margin is considered
	in calculating its outer size.</p>
   <p>When a box <a data-link-type="dfn" href="https://drafts.csswg.org/css-break-3/#fragment" id="ref-for-fragment">fragments</a>,
	step sizing is applied per fragment.</p>
   <h3 class="heading settled" data-level="2.2" id="block-step-insert"><span class="secno">2.2. </span><span class="content">Specifying the Spacing Type: the <a class="property" data-link-type="propdesc" href="#propdef-block-step-insert" id="ref-for-propdef-block-step-insert①">block-step-insert</a> property</span><a class="self-link" href="#block-step-insert"></a></h3>
   <table class="def propdef" data-link-for-hint="block-step-insert">
    <tbody>
     <tr>
      <th>Name:
      <td><dfn class="dfn-paneled css" data-dfn-type="property" data-export id="propdef-block-step-insert">block-step-insert</dfn>
     <tr class="value">
      <th><a href="https://drafts.csswg.org/css-values/#value-defs">Value:</a>
      <td class="prod">margin <a data-link-type="grammar" href="https://drafts.csswg.org/css-values-4/#comb-one" id="ref-for-comb-one①">|</a> padding 
     <tr>
      <th><a href="https://drafts.csswg.org/css-cascade/#initial-values">Initial:</a>
      <td>margin 
     <tr>
      <th>Applies to:
      <td>block-level boxes 
     <tr>
      <th><a href="https://drafts.csswg.org/css-cascade/#inherited-property">Inherited:</a>
      <td>no 
     <tr>
      <th><a href="https://drafts.csswg.org/css-values/#percentages">Percentages:</a>
      <td>N/A 
     <tr>
      <th><a href="https://drafts.csswg.org/css-cascade/#computed">Computed value:</a>
      <td>specified keyword 
     <tr>
      <th>Canonical order:
      <td>per grammar 
     <tr>
      <th><a href="https://drafts.csswg.org/web-animations/#animation-type">Animatable:</a>
      <td>no 
     <tr>
      <th><a href="https://drafts.csswg.org/web-animations/#animation-type">Animation type:</a>
      <td>discrete 
   </table>
   <p>This property specifies whether extra spacing
	derived from applying <a class="property" data-link-type="propdesc" href="#propdef-block-step-size" id="ref-for-propdef-block-step-size③">block-step-size</a> is inserted inside (like <a class="property" data-link-type="propdesc" href="https://drafts.csswg.org/css-box-3/#propdef-padding" id="ref-for-propdef-padding">padding</a>) or outside (like <a class="property" data-link-type="propdesc" href="https://drafts.csswg.org/css-box-3/#propdef-margin" id="ref-for-propdef-margin">margin</a>)
	the box’s border.</p>
   <p>Values have the following meanings:</p>
   <dl>
    <dt><dfn class="dfn-paneled css" data-dfn-for="block-step-insert" data-dfn-type="value" data-export id="valdef-block-step-insert-margin">margin</dfn> 
    <dd> Any extra space resulting from a <a class="property" data-link-type="propdesc" href="#propdef-block-step-size" id="ref-for-propdef-block-step-size④">block-step-size</a>-induced adjustment
			is inserted outside the box’s border, as extra margin. 
    <dt><dfn class="css" data-dfn-for="block-step-insert" data-dfn-type="value" data-export id="valdef-block-step-insert-padding">padding<a class="self-link" href="#valdef-block-step-insert-padding"></a></dfn> 
    <dd> Any extra space resulting from a <a class="property" data-link-type="propdesc" href="#propdef-block-step-size" id="ref-for-propdef-block-step-size⑤">block-step-size</a>-induced adjustment
			is inserted inside the box’s border, as extra padding. 
   </dl>
   <h3 class="heading settled" data-level="2.3" id="block-step-align"><span class="secno">2.3. </span><span class="content">Specifying Alignment: the <a class="property" data-link-type="propdesc" href="#propdef-block-step-align" id="ref-for-propdef-block-step-align①">block-step-align</a> property</span><a class="self-link" href="#block-step-align"></a></h3>
   <table class="def propdef" data-link-for-hint="block-step-align">
    <tbody>
     <tr>
      <th>Name:
      <td><dfn class="dfn-paneled css" data-dfn-type="property" data-export id="propdef-block-step-align">block-step-align</dfn>
     <tr class="value">
      <th><a href="https://drafts.csswg.org/css-values/#value-defs">Value:</a>
      <td class="prod">auto <a data-link-type="grammar" href="https://drafts.csswg.org/css-values-4/#comb-one" id="ref-for-comb-one②">|</a> center <span id="ref-for-comb-one③">|</span> start <span id="ref-for-comb-one④">|</span> end 
     <tr>
      <th><a href="https://drafts.csswg.org/css-cascade/#initial-values">Initial:</a>
      <td>auto 
     <tr>
      <th>Applies to:
      <td>block-level boxes 
     <tr>
      <th><a href="https://drafts.csswg.org/css-cascade/#inherited-property">Inherited:</a>
      <td>no 
     <tr>
      <th><a href="https://drafts.csswg.org/css-values/#percentages">Percentages:</a>
      <td>N/A 
     <tr>
      <th><a href="https://drafts.csswg.org/css-cascade/#computed">Computed value:</a>
      <td>specified keyword 
     <tr>
      <th>Canonical order:
      <td>per grammar 
     <tr>
      <th><a href="https://drafts.csswg.org/web-animations/#animation-type">Animatable:</a>
      <td>no 
     <tr>
      <th><a href="https://drafts.csswg.org/web-animations/#animation-type">Animation type:</a>
      <td>discrete 
   </table>
   <p>This property specifies whether extra spacing
	derived from applying <a class="property" data-link-type="propdesc" href="#propdef-block-step-size" id="ref-for-propdef-block-step-size⑥">block-step-size</a> is inserted before, inserted after, or split between both sides of the box.</p>
   <p>Values have the following meanings:</p>
   <dl>
    <dt><dfn class="css" data-dfn-for="block-step-align" data-dfn-type="value" data-export id="valdef-block-step-align-auto">auto<a class="self-link" href="#valdef-block-step-align-auto"></a></dfn> 
    <dd> If <a class="property" data-link-type="propdesc" href="#propdef-block-step-insert" id="ref-for-propdef-block-step-insert②">block-step-insert</a> is <a class="css" data-link-type="maybe" href="#valdef-block-step-insert-margin" id="ref-for-valdef-block-step-insert-margin">margin</a>:
			if <a class="property" data-link-type="propdesc" href="https://drafts.csswg.org/css-align-3/#propdef-align-self" id="ref-for-propdef-align-self">align-self</a> is <a class="css" data-link-type="maybe" href="#valdef-block-step-align-start" id="ref-for-valdef-block-step-align-start">start</a>, <a class="css" data-link-type="maybe" href="#valdef-block-step-align-end" id="ref-for-valdef-block-step-align-end">end</a>, or <a class="css" data-link-type="maybe" href="#valdef-block-step-align-center" id="ref-for-valdef-block-step-align-center">center</a>, treat as that value,
			otherwise treat as <span class="css" id="ref-for-valdef-block-step-align-center①">center</span>. 
    <dt><dfn class="dfn-paneled css" data-dfn-for="block-step-align" data-dfn-type="value" data-export id="valdef-block-step-align-center">center</dfn> 
    <dd> Any extra space resulting from a <a class="property" data-link-type="propdesc" href="#propdef-block-step-size" id="ref-for-propdef-block-step-size⑦">block-step-size</a>-induced adjustment
			is split, and applied half on either side of the box. 
    <dt><dfn class="dfn-paneled css" data-dfn-for="block-step-align" data-dfn-type="value" data-export id="valdef-block-step-align-start">start</dfn> 
    <dd> Any extra space resulting from a <a class="property" data-link-type="propdesc" href="#propdef-block-step-size" id="ref-for-propdef-block-step-size⑧">block-step-size</a>-induced adjustment
			is inserted on the <a data-link-type="dfn" href="https://drafts.csswg.org/css-writing-modes-4/#end" id="ref-for-end">end</a> side of the box. 
    <dt><dfn class="dfn-paneled css" data-dfn-for="block-step-align" data-dfn-type="value" data-export id="valdef-block-step-align-end">end</dfn> 
    <dd> Any extra space resulting from a <a class="property" data-link-type="propdesc" href="#propdef-block-step-size" id="ref-for-propdef-block-step-size⑨">block-step-size</a>-induced adjustment
			is inserted on the <a data-link-type="dfn" href="https://drafts.csswg.org/css-writing-modes-4/#start" id="ref-for-start">start</a> side of the box. 
   </dl>
   <p>In all cases,
	additional spacing cannot be added to margins
	that are truncated or omitted due to unforced fragmentation breaks
	(see <a data-link-type="biblio" href="#biblio-css3-page">[CSS3-PAGE]</a> and <a data-link-type="biblio" href="#biblio-css-break-3">[CSS-BREAK-3]</a>);
	therefore if <a class="property" data-link-type="propdesc" href="#propdef-block-step-insert" id="ref-for-propdef-block-step-insert③">block-step-insert</a> is <a class="css" data-link-type="maybe" href="#valdef-block-step-insert-margin" id="ref-for-valdef-block-step-insert-margin①">margin</a>,
	all extra space derived from applying <a class="property" data-link-type="propdesc" href="#propdef-block-step-size" id="ref-for-propdef-block-step-size①⓪">block-step-size</a> must be inserted on the opposite side of the fragment
	(regardless of <a class="property" data-link-type="propdesc" href="#propdef-block-step-align" id="ref-for-propdef-block-step-align②">block-step-align</a>).</p>
   <h3 class="heading settled" data-level="2.4" id="block-step-round"><span class="secno">2.4. </span><span class="content">Rounding Method: the <a class="property" data-link-type="propdesc" href="#propdef-block-step-round" id="ref-for-propdef-block-step-round②">block-step-round</a> property</span><a class="self-link" href="#block-step-round"></a></h3>
   <table class="def propdef" data-link-for-hint="block-step-round">
    <tbody>
     <tr>
      <th>Name:
      <td><dfn class="dfn-paneled css" data-dfn-type="property" data-export id="propdef-block-step-round">block-step-round</dfn>
     <tr class="value">
      <th><a href="https://drafts.csswg.org/css-values/#value-defs">Value:</a>
      <td class="prod">up <a data-link-type="grammar" href="https://drafts.csswg.org/css-values-4/#comb-one" id="ref-for-comb-one⑤">|</a> down <span id="ref-for-comb-one⑥">|</span> nearest 
     <tr>
      <th><a href="https://drafts.csswg.org/css-cascade/#initial-values">Initial:</a>
      <td>up 
     <tr>
      <th>Applies to:
      <td>block-level boxes 
     <tr>
      <th><a href="https://drafts.csswg.org/css-cascade/#inherited-property">Inherited:</a>
      <td>no 
     <tr>
      <th><a href="https://drafts.csswg.org/css-values/#percentages">Percentages:</a>
      <td>N/A 
     <tr>
      <th><a href="https://drafts.csswg.org/css-cascade/#computed">Computed value:</a>
      <td>specified keyword 
     <tr>
      <th>Canonical order:
      <td>per grammar 
     <tr>
      <th><a href="https://drafts.csswg.org/web-animations/#animation-type">Animatable:</a>
      <td>no 
     <tr>
      <th><a href="https://drafts.csswg.org/web-animations/#animation-type">Animation type:</a>
      <td>discrete 
   </table>
   <p>This property specifies whether adjustments due to <a class="property" data-link-type="propdesc" href="#propdef-block-step-size" id="ref-for-propdef-block-step-size①①">block-step-size</a> insert positive or negative space.</p>
   <p>Values have the following meanings:</p>
   <dl>
    <dt><dfn class="dfn-paneled css" data-dfn-for="block-step-align" data-dfn-type="value" data-export id="valdef-block-step-align-up">up</dfn> 
    <dd> The outer size of the box is <em>increased</em> (positive space is inserted)
			to fulfill the <a class="property" data-link-type="propdesc" href="#propdef-block-step-size" id="ref-for-propdef-block-step-size①②">block-step-size</a> constraint. 
    <dt><dfn class="dfn-paneled css" data-dfn-for="block-step-align" data-dfn-type="value" data-export id="valdef-block-step-align-down">down</dfn> 
    <dd> The outer size of the box is <em>decreased</em> (negative space is inserted)
			to fulfill the <a class="property" data-link-type="propdesc" href="#propdef-block-step-size" id="ref-for-propdef-block-step-size①③">block-step-size</a> constraint. 
    <dt><dfn class="css" data-dfn-for="block-step-align" data-dfn-type="value" data-export id="valdef-block-step-align-nearest">nearest<a class="self-link" href="#valdef-block-step-align-nearest"></a></dfn> 
    <dd> The outer size of the box is either <em>increased</em> (as for <a class="css" data-link-type="maybe" href="#valdef-block-step-align-up" id="ref-for-valdef-block-step-align-up">up</a>) or <em>decreased</em> (as for <a class="css" data-link-type="maybe" href="#valdef-block-step-align-down" id="ref-for-valdef-block-step-align-down">down</a>—<wbr>whichever results in the smallest absolute change—<wbr>to fulfill the <a class="property" data-link-type="propdesc" href="#propdef-block-step-size" id="ref-for-propdef-block-step-size①④">block-step-size</a> constraint.
			If both options would result in the same amount of change,
			the size is increased. 
   </dl>
   <h3 class="heading settled" data-level="2.5" id="block-step"><span class="secno">2.5. </span><span class="content">Block Step Adjustment Shorthand: the <a class="property" data-link-type="propdesc" href="#propdef-block-step" id="ref-for-propdef-block-step④">block-step</a> shorthand</span><a class="self-link" href="#block-step"></a></h3>
   <table class="def propdef" data-link-for-hint="block-step">
    <tbody>
     <tr>
      <th>Name:
      <td><dfn class="dfn-paneled css" data-dfn-type="property" data-export id="propdef-block-step">block-step</dfn>
     <tr class="value">
      <th><a href="https://drafts.csswg.org/css-values/#value-defs">Value:</a>
      <td class="prod"><a class="production" data-link-type="propdesc" href="#propdef-block-step-size" id="ref-for-propdef-block-step-size①⑤">&lt;'block-step-size'></a> <a data-link-type="grammar" href="https://drafts.csswg.org/css-values-4/#comb-any" id="ref-for-comb-any">||</a> <a class="production" data-link-type="propdesc" href="#propdef-block-step-insert" id="ref-for-propdef-block-step-insert④">&lt;'block-step-insert'></a> <span id="ref-for-comb-any①">||</span> <a class="production" data-link-type="propdesc" href="#propdef-block-step-align" id="ref-for-propdef-block-step-align③">&lt;'block-step-align'></a> <span id="ref-for-comb-any②">||</span> <a class="production" data-link-type="propdesc" href="#propdef-block-step-round" id="ref-for-propdef-block-step-round③">&lt;'block-step-round'></a> 
     <tr>
      <th><a href="https://drafts.csswg.org/css-cascade/#initial-values">Initial:</a>
      <td>see individual properties 
     <tr>
      <th>Applies to:
      <td>block-level boxes 
     <tr>
      <th><a href="https://drafts.csswg.org/css-cascade/#inherited-property">Inherited:</a>
      <td>no 
     <tr>
      <th><a href="https://drafts.csswg.org/css-values/#percentages">Percentages:</a>
      <td>N/A 
     <tr>
      <th><a href="https://drafts.csswg.org/css-cascade/#computed">Computed value:</a>
      <td>see individual properties 
     <tr>
      <th><a href="https://drafts.csswg.org/web-animations/#animation-type">Animation type:</a>
      <td>see individual properties 
     <tr>
      <th>Canonical order:
      <td>per grammar 
   </table>
   <p>This <a data-link-type="dfn" href="https://drafts.csswg.org/css-cascade-4/#shorthand-property" id="ref-for-shorthand-property">shorthand property</a> allows for setting <a class="property" data-link-type="propdesc" href="#propdef-block-step-size" id="ref-for-propdef-block-step-size①⑥">block-step-size</a>, <a class="property" data-link-type="propdesc" href="#propdef-block-step-insert" id="ref-for-propdef-block-step-insert⑤">block-step-insert</a>, <a class="property" data-link-type="propdesc" href="#propdef-block-step-align" id="ref-for-propdef-block-step-align④">block-step-align</a>,
	and <a class="property" data-link-type="propdesc" href="#propdef-block-step-round" id="ref-for-propdef-block-step-round④">block-step-round</a> in one declaration.
	Omitted values are set to the property’s initial value.</p>
   <p><strong class="advisement"> Authors are advised to use this shorthand rather than the longhands
	unless there is a specific need for its individual longhands to cascade independently.</strong></p>
   <h2 class="heading settled" data-level="3" id="line-height-step"><span class="secno">3. </span><span class="content">Adjusting Line Box Heights: the <a class="property" data-link-type="propdesc" href="#propdef-line-height-step" id="ref-for-propdef-line-height-step②">line-height-step</a> property</span><a class="self-link" href="#line-height-step"></a></h2>
   <table class="def propdef" data-link-for-hint="line-height-step">
    <tbody>
     <tr>
      <th>Name:
      <td><dfn class="dfn-paneled css" data-dfn-type="property" data-export id="propdef-line-height-step">line-height-step</dfn>
     <tr class="value">
      <th><a href="https://drafts.csswg.org/css-values/#value-defs">Value:</a>
      <td class="prod"><a class="production css" data-link-type="type" href="https://drafts.csswg.org/css-values-3/#length-value" id="ref-for-length-value③" title="Expands to: em | vb | ch | cm | vh | vi | in | ex | vw | ic | pt | px | lh | pc | rem | rlh | vmax | advance measure | vmin | mm | cap | q">&lt;length></a> 
     <tr>
      <th><a href="https://drafts.csswg.org/css-cascade/#initial-values">Initial:</a>
      <td>0px 
     <tr>
      <th>Applies to:
      <td>block containers 
     <tr>
      <th><a href="https://drafts.csswg.org/css-cascade/#inherited-property">Inherited:</a>
      <td>yes 
     <tr>
      <th><a href="https://drafts.csswg.org/css-values/#percentages">Percentages:</a>
      <td>N/A 
     <tr>
      <th><a href="https://drafts.csswg.org/css-cascade/#computed">Computed value:</a>
      <td>absolute length 
     <tr>
      <th>Canonical order:
      <td>per grammar 
     <tr>
      <th><a href="https://drafts.csswg.org/web-animations/#animation-type">Animatable:</a>
      <td>no 
     <tr>
      <th><a href="https://drafts.csswg.org/web-animations/#animation-type">Animation type:</a>
      <td>by computed value type 
   </table>
   <p>This property defines the <dfn class="dfn-paneled" data-dfn-type="dfn" data-noexport id="step-unit">step unit</dfn> for line box heights.
A <a data-link-type="dfn" href="#step-unit" id="ref-for-step-unit②">step unit</a> is the length of the vertical rhythm,
usually the distance from one baseline to the next baseline of the body text.
Body text should fit into one <span id="ref-for-step-unit③">step unit</span>,
and taller lines such as headings
should have heights of two or more <span id="ref-for-step-unit④">step unit</span>s.
Vertical rhythm is created
by making heights of all lines an integer multiple of the <span id="ref-for-step-unit⑤">step unit</span>.</p>
   <p>When the <a data-link-type="dfn" href="#step-unit" id="ref-for-step-unit⑥">step unit</a> is set to a positive <a class="production css" data-link-type="type" href="https://drafts.csswg.org/css-values-3/#length-value" id="ref-for-length-value④" title="Expands to: em | vb | ch | cm | vh | vi | in | ex | vw | ic | pt | px | lh | pc | rem | rlh | vmax | advance measure | vmin | mm | cap | q">&lt;length></a>,
	the line box heights are rounded <i>up</i> to
	the closest multiple of the unit.
	Negative <span class="production" id="ref-for-length-value⑤" title="Expands to: em | vb | ch | cm | vh | vi | in | ex | vw | ic | pt | px | lh | pc | rem | rlh | vmax | advance measure | vmin | mm | cap | q">&lt;length></span> values are invalid.</p>
   <p><a data-link-type="biblio" href="#biblio-css21">[CSS21]</a> <a href="https://drafts.csswg.org/css2/visudet.html#line-height">§10.8 Line height calculations</a> defines how to compute the height of a line box from its inline-level content.
	The rounding is applied to the resulting height of the line box,
	and the additional space is distributed to <a data-link-type="dfn" href="https://drafts.csswg.org/css-writing-modes-4/#over" id="ref-for-over">over</a>-side and <a data-link-type="dfn" href="https://drafts.csswg.org/css-writing-modes-4/#under" id="ref-for-under">under</a>-side of the line box equally,
	so that the original line box appears at the center of the
	multiple of <a data-link-type="dfn" href="#step-unit" id="ref-for-step-unit⑦">step unit</a>.
	This adjustment is done
	by assuming that there is an inline-level box that has adjusted A' and D'
	in the line box.
	This inline-level box does not affect alignment points of the <a class="property" data-link-type="propdesc" href="https://drafts.csswg.org/css-inline-3/#propdef-vertical-align" id="ref-for-propdef-vertical-align">vertical-align</a> property,
	except values that align relative to the line box.</p>
   <div class="figure">
     <img src="images/adjust-line-height.svg"> 
    <p class="caption">Rounding up the computed line box height. </p>
   </div>
   <div class="issue" id="issue-27b8d19f"><a class="self-link" href="#issue-27b8d19f"></a>Should this be animatable?
	There doesn’t seem to be use cases but needed for consistency?</div>
   <div class="example" id="example-1ffcd486">
    <a class="self-link" href="#example-1ffcd486"></a> 
    <div class="figure" style="float:right"> <img U0003Cblockquote src="images/line-grid-center.svg" style="height: 300px"> </div>
    <p>In the following example,
		the height of line box in each paragraph is rounded up to the <a data-link-type="dfn" href="#step-unit" id="ref-for-step-unit⑧">step unit</a>.</p>
<pre class="lang-css highlight"><c- f>:root </c-><c- p>{</c->
  <c- k>font-size</c-><c- p>:</c-> <c- m>12</c-><c- l>pt</c-><c- p>;</c->
  <c- k>--my-grid</c-><c- p>:</c-> <c- m>18</c-><c- l>pt</c-><c- p>;</c->
  <c- k>line-height-step</c-><c- p>:</c-> <c- nf>var</c-><c- p>(</c->--my-grid<c- p>);</c->
<c- p>}</c->
<c- f>h1 </c-><c- p>{</c->
  <c- k>font-size</c-><c- p>:</c-> <c- m>20</c-><c- l>pt</c-><c- p>;</c->
  <c- k>margin-top</c-><c- p>:</c-> <c- nf>calc</c-><c- p>(</c-><c- m>2</c-> * var(--my-grid));
}
p {
  margin: 0;
}
</pre>
    <p>The line box in <code>&lt;h1></code> does not fit into one <a data-link-type="dfn" href="#step-unit" id="ref-for-step-unit⑨">step unit</a> and thus occupies two,
		but it is still centered within the two <span id="ref-for-step-unit①⓪">step unit</span>.</p>
   </div>
   <div class="example" id="example-819d7b57">
    <a class="self-link" href="#example-819d7b57"></a> Authors can keep margins or other properties to be multiple of <a data-link-type="dfn" href="#step-unit" id="ref-for-step-unit①①">step unit</a> using <a class="css" data-link-type="maybe" href="https://drafts.csswg.org/css-variables-1/#funcdef-var" id="ref-for-funcdef-var">var()</a> and <a class="css" data-link-type="maybe" href="https://drafts.csswg.org/css-values-4/#funcdef-calc" id="ref-for-funcdef-calc">calc()</a> as in the example above. 
    <p>If author prefers,
	tools like Sass can make such declarations shorter.</p>
<pre class="lang-css highlight"><c- f>$gu: 18px;</c->

<c- f>@function gu($n) </c-><c- p>{</c->
  <c- n>@return</c-> $n * $gu;
}

h1 {
  font-size: 20pt;
  margin: gu(1.2) auto gu(1.8);
}
</pre>
   </div>
   <div class="note" role="note"> It is usually recommended to set the <a class="property" data-link-type="propdesc" href="https://drafts.csswg.org/css2/visudet.html#propdef-line-height" id="ref-for-propdef-line-height">line-height</a> lower than
	the <a data-link-type="dfn" href="#step-unit" id="ref-for-step-unit①②">step unit</a>.
	The used line height can increase due to several factors such as
	the use of <a class="property" data-link-type="propdesc" href="https://drafts.csswg.org/css-inline-3/#propdef-vertical-align" id="ref-for-propdef-vertical-align①">vertical-align</a> or font fallback. </div>
   <h2 class="heading settled" data-level="4" id="priv-sec"><span class="secno">4. </span><span class="content">Privacy and Security Considerations</span><a class="self-link" href="#priv-sec"></a></h2>
   <p>This specification introduces no new privacy leaks,
	or security considerations beyond "implement it correctly".</p>
   <h2 class="heading settled" data-level="5" id="acks"><span class="secno">5. </span><span class="content">Acknowledgments</span><a class="self-link" href="#acks"></a></h2>
   <p>This specification would not have been possible without the help from:
	Masaharu Akutsu,
	Yoko Aoki,
	Takao Baba,
	Chris Eppstein,
	Ichiro Inaba,
	Jxck,
	Noriko Kase,
	Motoya Kinoshita,
	Shinyu Murakami,
	Tsutomu Nanjo,
	Kiyoshi Narishima,
	Charlie Neely,
	Takuya Nishimura,
	Katsuhiro Osumi,
	Florian Rivoal,
	Hiroshi Sakakibara,
	Alan Stearns,
	Masataka Yakura,
	KADOKAWA Corporation,
	PixelGrid Inc.,
	and the CSS Working Group members.</p>
  </main>
  <h2 class="no-ref no-num heading settled" id="conformance"><span class="content"> Conformance</span><a class="self-link" href="#conformance"></a></h2>
  <h3 class="heading settled" id="document-conventions"><span class="content"> Document conventions</span><a class="self-link" href="#document-conventions"></a></h3>
  <p>Conformance requirements are expressed with a combination of
	descriptive assertions and RFC 2119 terminology. The key words “MUST”,
	“MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”,
	“RECOMMENDED”, “MAY”, and “OPTIONAL” in the normative parts of this
	document are to be interpreted as described in RFC 2119.
	However, for readability, these words do not appear in all uppercase
	letters in this specification. </p>
  <p>All of the text of this specification is normative except sections
	explicitly marked as non-normative, examples, and notes. <a data-link-type="biblio" href="#biblio-rfc2119">[RFC2119]</a> </p>
  <p>Examples in this specification are introduced with the words “for example”
	or are set apart from the normative text with <code>class="example"</code>,
	like this: </p>
  <div class="example" id="example-ae2b6bc0">
   <a class="self-link" href="#example-ae2b6bc0"></a> 
   <p>This is an example of an informative example. </p>
  </div>
  <p>Informative notes begin with the word “Note” and are set apart from the
	normative text with <code>class="note"</code>, like this: </p>
  <p class="note" role="note">Note, this is an informative note. </p>
  <p>Advisements are normative sections styled to evoke special attention and are
	set apart from other normative text with <code>&lt;strong class="advisement"></code>, like
	this: <strong class="advisement"> UAs MUST provide an accessible alternative. </strong> </p>
  <h3 class="heading settled" id="conform-classes"><span class="content"> Conformance classes</span><a class="self-link" href="#conform-classes"></a></h3>
  <p>Conformance to this specification
	is defined for three conformance classes: </p>
  <dl>
   <dt>style sheet 
   <dd>A <a href="http://www.w3.org/TR/CSS2/conform.html#style-sheet">CSS
			style sheet</a>. 
   <dt>renderer 
   <dd>A <a href="http://www.w3.org/TR/CSS2/conform.html#user-agent">UA</a> that interprets the semantics of a style sheet and renders
			documents that use them. 
   <dt>authoring tool 
   <dd>A <a href="http://www.w3.org/TR/CSS2/conform.html#user-agent">UA</a> that writes a style sheet. 
  </dl>
  <p>A style sheet is conformant to this specification
	if all of its statements that use syntax defined in this module are valid
	according to the generic CSS grammar and the individual grammars of each
	feature defined in this module. </p>
  <p>A renderer is conformant to this specification
	if, in addition to interpreting the style sheet as defined by the
	appropriate specifications, it supports all the features defined
	by this specification by parsing them correctly
	and rendering the document accordingly. However, the inability of a
	UA to correctly render a document due to limitations of the device
	does not make the UA non-conformant. (For example, a UA is not
	required to render color on a monochrome monitor.) </p>
  <p>An authoring tool is conformant to this specification
	if it writes style sheets that are syntactically correct according to the
	generic CSS grammar and the individual grammars of each feature in
	this module, and meet all other conformance requirements of style sheets
	as described in this module. </p>
  <h3 class="heading settled" id="conform-responsible"><span class="content"> Requirements for Responsible Implementation of CSS</span><a class="self-link" href="#conform-responsible"></a></h3>
  <p>The following sections define several conformance requirements
		for implementing CSS responsibly,
		in a way that promotes interoperability in the present and future. </p>
  <h4 class="heading settled" id="conform-partial"><span class="content"> Partial Implementations</span><a class="self-link" href="#conform-partial"></a></h4>
  <p>So that authors can exploit the forward-compatible parsing rules to assign fallback values, <strong>CSS renderers <em>must</em> treat as invalid
		(and <a href="http://www.w3.org/TR/CSS2/conform.html#ignore">ignore as appropriate</a>)
		any at-rules, properties, property values, keywords, and other syntactic constructs
		for which they have no usable level of support</strong>.
		In particular, user agents <em>must not</em> selectively ignore
		unsupported property values and honor supported values in a single multi-value property declaration:
		if any value is considered invalid (as unsupported values must be),
		CSS requires that the entire declaration be ignored. </p>
  <h4 class="heading settled" id="conform-future-proofing"><span class="content"> Implementations of Unstable and Proprietary Features</span><a class="self-link" href="#conform-future-proofing"></a></h4>
  <p>To avoid clashes with future stable CSS features,
		the CSSWG recommends <a href="http://www.w3.org/TR/CSS/#future-proofing">following best practices</a> for the implementation of <a href="http://www.w3.org/TR/CSS/#unstable">unstable</a> features and <a href="http://www.w3.org/TR/CSS/#proprietary-extension">proprietary extensions</a> to CSS. </p>
  <h4 class="heading settled" id="conform-testing"><span class="content"> Implementations of CR-level Features</span><a class="self-link" href="#conform-testing"></a></h4>
  <p>Once a specification reaches the Candidate Recommendation stage,
		implementers should release an <a data-link-type="dfn" href="http://www.w3.org/TR/CSS/#vendor-prefix">unprefixed</a> implementation
		of any CR-level feature they can demonstrate
		to be correctly implemented according to spec,
		and should avoid exposing a prefixed variant of that feature. </p>
  <p>To establish and maintain the interoperability of CSS across
		implementations, the CSS Working Group requests that non-experimental
		CSS renderers submit an implementation report (and, if necessary, the
		testcases used for that implementation report) to the W3C before
		releasing an unprefixed implementation of any CSS features. Testcases
		submitted to W3C are subject to review and correction by the CSS
		Working Group. </p>
  <p>
   Further information on submitting testcases and implementation reports
		can be found from on the CSS Working Group’s website at <a href="http://www.w3.org/Style/CSS/Test/">http://www.w3.org/Style/CSS/Test/</a>.
		Questions should be directed to the <a href="http://lists.w3.org/Archives/Public/public-css-testsuite">public-css-testsuite@w3.org</a> mailing list. 
<script src="https://www.w3.org/scripts/TR/2016/fixup.js"></script>
  </p>
  <h2 class="no-num no-ref heading settled" id="index"><span class="content">Index</span><a class="self-link" href="#index"></a></h2>
  <h3 class="no-num no-ref heading settled" id="index-defined-here"><span class="content">Terms defined by this specification</span><a class="self-link" href="#index-defined-here"></a></h3>
  <ul class="index">
   <li><a href="#valdef-block-step-align-auto">auto</a><span>, in §2.3</span>
   <li><a href="#propdef-block-step">block-step</a><span>, in §2.5</span>
   <li><a href="#propdef-block-step-align">block-step-align</a><span>, in §2.3</span>
   <li><a href="#propdef-block-step-insert">block-step-insert</a><span>, in §2.2</span>
   <li><a href="#propdef-block-step-round">block-step-round</a><span>, in §2.4</span>
   <li><a href="#propdef-block-step-size">block-step-size</a><span>, in §2.1</span>
   <li><a href="#valdef-block-step-align-center">center</a><span>, in §2.3</span>
   <li><a href="#valdef-block-step-align-down">down</a><span>, in §2.4</span>
   <li><a href="#valdef-block-step-align-end">end</a><span>, in §2.3</span>
   <li><a href="#propdef-line-height-step">line-height-step</a><span>, in §3</span>
   <li><a href="#valdef-block-step-insert-margin">margin</a><span>, in §2.2</span>
   <li><a href="#valdef-block-step-align-nearest">nearest</a><span>, in §2.4</span>
   <li><a href="#valdef-block-step-insert-padding">padding</a><span>, in §2.2</span>
   <li><a href="#valdef-block-step-align-start">start</a><span>, in §2.3</span>
   <li><a href="#step-unit">step unit</a><span>, in §3</span>
   <li><a href="#valdef-block-step-align-up">up</a><span>, in §2.4</span>
  </ul>
  <aside class="dfn-panel" data-for="term-for-propdef-align-self">
   <a href="https://drafts.csswg.org/css-align-3/#propdef-align-self">https://drafts.csswg.org/css-align-3/#propdef-align-self</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-propdef-align-self">2.3. Specifying Alignment: the block-step-align property</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="term-for-propdef-margin">
   <a href="https://drafts.csswg.org/css-box-3/#propdef-margin">https://drafts.csswg.org/css-box-3/#propdef-margin</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-propdef-margin">2.2. Specifying the Spacing Type: the block-step-insert property</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="term-for-propdef-padding">
   <a href="https://drafts.csswg.org/css-box-3/#propdef-padding">https://drafts.csswg.org/css-box-3/#propdef-padding</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-propdef-padding">2.2. Specifying the Spacing Type: the block-step-insert property</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="term-for-fragment">
   <a href="https://drafts.csswg.org/css-break-3/#fragment">https://drafts.csswg.org/css-break-3/#fragment</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-fragment">2.1. Specifying the Step Size: the block-step-size property</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="term-for-shorthand-property">
   <a href="https://drafts.csswg.org/css-cascade-4/#shorthand-property">https://drafts.csswg.org/css-cascade-4/#shorthand-property</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-shorthand-property">2.5. Block Step Adjustment Shorthand: the block-step shorthand</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="term-for-establish-an-independent-formatting-context">
   <a href="https://drafts.csswg.org/css-display-3/#establish-an-independent-formatting-context">https://drafts.csswg.org/css-display-3/#establish-an-independent-formatting-context</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-establish-an-independent-formatting-context">2.1. Specifying the Step Size: the block-step-size property</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="term-for-propdef-vertical-align">
   <a href="https://drafts.csswg.org/css-inline-3/#propdef-vertical-align">https://drafts.csswg.org/css-inline-3/#propdef-vertical-align</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-propdef-vertical-align">3. Adjusting Line Box Heights: the line-height-step property</a> <a href="#ref-for-propdef-vertical-align①">(2)</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="term-for-propdef-line-grid">
   <a href="https://drafts.csswg.org/css-line-grid-1/#propdef-line-grid">https://drafts.csswg.org/css-line-grid-1/#propdef-line-grid</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-propdef-line-grid">1.1. East Asian Casual Vertical Rhythms</a> <a href="#ref-for-propdef-line-grid①">(2)</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="term-for-length-value">
   <a href="https://drafts.csswg.org/css-values-3/#length-value">https://drafts.csswg.org/css-values-3/#length-value</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-length-value">2.1. Specifying the Step Size: the block-step-size property</a> <a href="#ref-for-length-value①">(2)</a> <a href="#ref-for-length-value②">(3)</a>
    <li><a href="#ref-for-length-value③">3. Adjusting Line Box Heights: the line-height-step property</a> <a href="#ref-for-length-value④">(2)</a> <a href="#ref-for-length-value⑤">(3)</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="term-for-funcdef-calc">
   <a href="https://drafts.csswg.org/css-values-4/#funcdef-calc">https://drafts.csswg.org/css-values-4/#funcdef-calc</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-funcdef-calc">3. Adjusting Line Box Heights: the line-height-step property</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="term-for-comb-one">
   <a href="https://drafts.csswg.org/css-values-4/#comb-one">https://drafts.csswg.org/css-values-4/#comb-one</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-comb-one">2.1. Specifying the Step Size: the block-step-size property</a>
    <li><a href="#ref-for-comb-one①">2.2. Specifying the Spacing Type: the block-step-insert property</a>
    <li><a href="#ref-for-comb-one②">2.3. Specifying Alignment: the block-step-align property</a> <a href="#ref-for-comb-one③">(2)</a> <a href="#ref-for-comb-one④">(3)</a>
    <li><a href="#ref-for-comb-one⑤">2.4. Rounding Method: the block-step-round property</a> <a href="#ref-for-comb-one⑥">(2)</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="term-for-comb-any">
   <a href="https://drafts.csswg.org/css-values-4/#comb-any">https://drafts.csswg.org/css-values-4/#comb-any</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-comb-any">2.5. Block Step Adjustment Shorthand: the block-step shorthand</a> <a href="#ref-for-comb-any①">(2)</a> <a href="#ref-for-comb-any②">(3)</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="term-for-funcdef-var">
   <a href="https://drafts.csswg.org/css-variables-1/#funcdef-var">https://drafts.csswg.org/css-variables-1/#funcdef-var</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-funcdef-var">3. Adjusting Line Box Heights: the line-height-step property</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="term-for-block-size">
   <a href="https://drafts.csswg.org/css-writing-modes-4/#block-size">https://drafts.csswg.org/css-writing-modes-4/#block-size</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-block-size">2.1. Specifying the Step Size: the block-step-size property</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="term-for-end">
   <a href="https://drafts.csswg.org/css-writing-modes-4/#end">https://drafts.csswg.org/css-writing-modes-4/#end</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-end">2.3. Specifying Alignment: the block-step-align property</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="term-for-over">
   <a href="https://drafts.csswg.org/css-writing-modes-4/#over">https://drafts.csswg.org/css-writing-modes-4/#over</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-over">3. Adjusting Line Box Heights: the line-height-step property</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="term-for-start">
   <a href="https://drafts.csswg.org/css-writing-modes-4/#start">https://drafts.csswg.org/css-writing-modes-4/#start</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-start">2.3. Specifying Alignment: the block-step-align property</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="term-for-under">
   <a href="https://drafts.csswg.org/css-writing-modes-4/#under">https://drafts.csswg.org/css-writing-modes-4/#under</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-under">3. Adjusting Line Box Heights: the line-height-step property</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="term-for-propdef-line-height">
   <a href="https://drafts.csswg.org/css2/visudet.html#propdef-line-height">https://drafts.csswg.org/css2/visudet.html#propdef-line-height</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-propdef-line-height">3. Adjusting Line Box Heights: the line-height-step property</a>
   </ul>
  </aside>
  <h3 class="no-num no-ref heading settled" id="index-defined-elsewhere"><span class="content">Terms defined by reference</span><a class="self-link" href="#index-defined-elsewhere"></a></h3>
  <ul class="index">
   <li>
    <a data-link-type="biblio">[css-align-3]</a> defines the following terms:
    <ul>
     <li><span class="dfn-paneled" id="term-for-propdef-align-self" style="color:initial">align-self</span>
    </ul>
   <li>
    <a data-link-type="biblio">[css-box-3]</a> defines the following terms:
    <ul>
     <li><span class="dfn-paneled" id="term-for-propdef-margin" style="color:initial">margin</span>
     <li><span class="dfn-paneled" id="term-for-propdef-padding" style="color:initial">padding</span>
    </ul>
   <li>
    <a data-link-type="biblio">[CSS-BREAK-3]</a> defines the following terms:
    <ul>
     <li><span class="dfn-paneled" id="term-for-fragment" style="color:initial">fragment</span>
    </ul>
   <li>
    <a data-link-type="biblio">[css-cascade-4]</a> defines the following terms:
    <ul>
     <li><span class="dfn-paneled" id="term-for-shorthand-property" style="color:initial">shorthand property</span>
    </ul>
   <li>
    <a data-link-type="biblio">[css-display-3]</a> defines the following terms:
    <ul>
     <li><span class="dfn-paneled" id="term-for-establish-an-independent-formatting-context" style="color:initial">establish an independent formatting context</span>
    </ul>
   <li>
    <a data-link-type="biblio">[css-inline-3]</a> defines the following terms:
    <ul>
     <li><span class="dfn-paneled" id="term-for-propdef-vertical-align" style="color:initial">vertical-align</span>
    </ul>
   <li>
    <a data-link-type="biblio">[css-line-grid-1]</a> defines the following terms:
    <ul>
     <li><span class="dfn-paneled" id="term-for-propdef-line-grid" style="color:initial">line-grid</span>
    </ul>
   <li>
    <a data-link-type="biblio">[css-values-3]</a> defines the following terms:
    <ul>
     <li><span class="dfn-paneled" id="term-for-length-value" style="color:initial">&lt;length></span>
    </ul>
   <li>
    <a data-link-type="biblio">[css-values-4]</a> defines the following terms:
    <ul>
     <li><span class="dfn-paneled" id="term-for-funcdef-calc" style="color:initial">calc()</span>
     <li><span class="dfn-paneled" id="term-for-comb-one" style="color:initial">|</span>
     <li><span class="dfn-paneled" id="term-for-comb-any" style="color:initial">||</span>
    </ul>
   <li>
    <a data-link-type="biblio">[css-variables-1]</a> defines the following terms:
    <ul>
     <li><span class="dfn-paneled" id="term-for-funcdef-var" style="color:initial">var()</span>
    </ul>
   <li>
    <a data-link-type="biblio">[css-writing-modes-4]</a> defines the following terms:
    <ul>
     <li><span class="dfn-paneled" id="term-for-block-size" style="color:initial">block size</span>
     <li><span class="dfn-paneled" id="term-for-end" style="color:initial">end</span>
     <li><span class="dfn-paneled" id="term-for-over" style="color:initial">over</span>
     <li><span class="dfn-paneled" id="term-for-start" style="color:initial">start</span>
     <li><span class="dfn-paneled" id="term-for-under" style="color:initial">under</span>
    </ul>
   <li>
    <a data-link-type="biblio">[CSS21]</a> defines the following terms:
    <ul>
     <li><span class="dfn-paneled" id="term-for-propdef-line-height" style="color:initial">line-height</span>
    </ul>
  </ul>
  <h2 class="no-num no-ref heading settled" id="references"><span class="content">References</span><a class="self-link" href="#references"></a></h2>
  <h3 class="no-num no-ref heading settled" id="normative"><span class="content">Normative References</span><a class="self-link" href="#normative"></a></h3>
  <dl>
   <dt id="biblio-css-align-3">[CSS-ALIGN-3]
   <dd>Elika Etemad; Tab Atkins Jr.. <a href="https://www.w3.org/TR/css-align-3/">CSS Box Alignment Module Level 3</a>. 6 December 2018. WD. URL: <a href="https://www.w3.org/TR/css-align-3/">https://www.w3.org/TR/css-align-3/</a>
   <dt id="biblio-css-box-3">[CSS-BOX-3]
   <dd>Elika Etemad. <a href="https://www.w3.org/TR/css-box-3/">CSS Box Model Module Level 3</a>. 18 December 2018. WD. URL: <a href="https://www.w3.org/TR/css-box-3/">https://www.w3.org/TR/css-box-3/</a>
   <dt id="biblio-css-break-3">[CSS-BREAK-3]
   <dd>Rossen Atanassov; Elika Etemad. <a href="https://www.w3.org/TR/css-break-3/">CSS Fragmentation Module Level 3</a>. 4 December 2018. CR. URL: <a href="https://www.w3.org/TR/css-break-3/">https://www.w3.org/TR/css-break-3/</a>
   <dt id="biblio-css-cascade-4">[CSS-CASCADE-4]
   <dd>Elika Etemad; Tab Atkins Jr.. <a href="https://www.w3.org/TR/css-cascade-4/">CSS Cascading and Inheritance Level 4</a>. 28 August 2018. CR. URL: <a href="https://www.w3.org/TR/css-cascade-4/">https://www.w3.org/TR/css-cascade-4/</a>
   <dt id="biblio-css-display-3">[CSS-DISPLAY-3]
   <dd>Tab Atkins Jr.; Elika Etemad. <a href="https://www.w3.org/TR/css-display-3/">CSS Display Module Level 3</a>. 28 August 2018. CR. URL: <a href="https://www.w3.org/TR/css-display-3/">https://www.w3.org/TR/css-display-3/</a>
   <dt id="biblio-css-inline-3">[CSS-INLINE-3]
   <dd>Dave Cramer; Elika Etemad; Steve Zilles. <a href="https://www.w3.org/TR/css-inline-3/">CSS Inline Layout Module Level 3</a>. 8 August 2018. WD. URL: <a href="https://www.w3.org/TR/css-inline-3/">https://www.w3.org/TR/css-inline-3/</a>
   <dt id="biblio-css-line-grid-1">[CSS-LINE-GRID-1]
   <dd>Elika Etemad; Koji Ishii; Alan Stearns. <a href="https://www.w3.org/TR/css-line-grid-1/">CSS Line Grid Module Level 1</a>. 16 September 2014. WD. URL: <a href="https://www.w3.org/TR/css-line-grid-1/">https://www.w3.org/TR/css-line-grid-1/</a>
   <dt id="biblio-css-values-3">[CSS-VALUES-3]
   <dd>Tab Atkins Jr.; Elika Etemad. <a href="https://www.w3.org/TR/css-values-3/">CSS Values and Units Module Level 3</a>. 31 January 2019. CR. URL: <a href="https://www.w3.org/TR/css-values-3/">https://www.w3.org/TR/css-values-3/</a>
   <dt id="biblio-css-values-4">[CSS-VALUES-4]
   <dd>Tab Atkins Jr.; Elika Etemad. <a href="https://www.w3.org/TR/css-values-4/">CSS Values and Units Module Level 4</a>. 31 January 2019. WD. URL: <a href="https://www.w3.org/TR/css-values-4/">https://www.w3.org/TR/css-values-4/</a>
   <dt id="biblio-css-writing-modes-4">[CSS-WRITING-MODES-4]
   <dd>Elika Etemad; Koji Ishii. <a href="https://www.w3.org/TR/css-writing-modes-4/">CSS Writing Modes Level 4</a>. 24 May 2018. CR. URL: <a href="https://www.w3.org/TR/css-writing-modes-4/">https://www.w3.org/TR/css-writing-modes-4/</a>
   <dt id="biblio-css21">[CSS21]
   <dd>Bert Bos; et al. <a href="https://www.w3.org/TR/CSS2/">Cascading Style Sheets Level 2 Revision 1 (CSS 2.1) Specification</a>. 7 June 2011. REC. URL: <a href="https://www.w3.org/TR/CSS2/">https://www.w3.org/TR/CSS2/</a>
   <dt id="biblio-rfc2119">[RFC2119]
   <dd>S. Bradner. <a href="https://tools.ietf.org/html/rfc2119">Key words for use in RFCs to Indicate Requirement Levels</a>. March 1997. Best Current Practice. URL: <a href="https://tools.ietf.org/html/rfc2119">https://tools.ietf.org/html/rfc2119</a>
  </dl>
  <h3 class="no-num no-ref heading settled" id="informative"><span class="content">Informative References</span><a class="self-link" href="#informative"></a></h3>
  <dl>
   <dt id="biblio-css-variables-1">[CSS-VARIABLES-1]
   <dd>Tab Atkins Jr.. <a href="https://www.w3.org/TR/css-variables-1/">CSS Custom Properties for Cascading Variables Module Level 1</a>. 3 December 2015. CR. URL: <a href="https://www.w3.org/TR/css-variables-1/">https://www.w3.org/TR/css-variables-1/</a>
   <dt id="biblio-css3-page">[CSS3-PAGE]
   <dd>Elika Etemad; Simon Sapin. <a href="https://www.w3.org/TR/css-page-3/">CSS Paged Media Module Level 3</a>. 18 October 2018. WD. URL: <a href="https://www.w3.org/TR/css-page-3/">https://www.w3.org/TR/css-page-3/</a>
  </dl>
  <h2 class="no-num no-ref heading settled" id="property-index"><span class="content">Property Index</span><a class="self-link" href="#property-index"></a></h2>
  <div class="big-element-wrapper">
   <table class="index">
    <thead>
     <tr>
      <th scope="col">Name
      <th scope="col">Value
      <th scope="col">Initial
      <th scope="col">Applies to
      <th scope="col">Inh.
      <th scope="col">%ages
      <th scope="col">Ani­mat­able
      <th scope="col">Anim­ation type
      <th scope="col">Canonical order
      <th scope="col">Com­puted value
    <tbody>
     <tr>
      <th scope="row"><a class="css" data-link-type="property" href="#propdef-block-step" id="ref-for-propdef-block-step⑤">block-step</a>
      <td>&lt;'block-step-size'> || &lt;'block-step-insert'> || &lt;'block-step-align'> || &lt;'block-step-round'>
      <td>see individual properties
      <td>block-level boxes
      <td>no
      <td>N/A
      <td>
      <td>see individual properties
      <td>per grammar
      <td>see individual properties
     <tr>
      <th scope="row"><a class="css" data-link-type="property" href="#propdef-block-step-align" id="ref-for-propdef-block-step-align⑤">block-step-align</a>
      <td>auto | center | start | end
      <td>auto
      <td>block-level boxes
      <td>no
      <td>N/A
      <td>no
      <td>discrete
      <td>per grammar
      <td>specified keyword
     <tr>
      <th scope="row"><a class="css" data-link-type="property" href="#propdef-block-step-insert" id="ref-for-propdef-block-step-insert⑥">block-step-insert</a>
      <td>margin | padding
      <td>margin
      <td>block-level boxes
      <td>no
      <td>N/A
      <td>no
      <td>discrete
      <td>per grammar
      <td>specified keyword
     <tr>
      <th scope="row"><a class="css" data-link-type="property" href="#propdef-block-step-round" id="ref-for-propdef-block-step-round⑤">block-step-round</a>
      <td>up | down | nearest
      <td>up
      <td>block-level boxes
      <td>no
      <td>N/A
      <td>no
      <td>discrete
      <td>per grammar
      <td>specified keyword
     <tr>
      <th scope="row"><a class="css" data-link-type="property" href="#propdef-block-step-size" id="ref-for-propdef-block-step-size①⑦">block-step-size</a>
      <td>none | &lt;length>
      <td>none
      <td>block-level boxes
      <td>no
      <td>N/A
      <td>???
      <td>by computed value type
      <td>per grammar
      <td>specified keyword or absolute length
     <tr>
      <th scope="row"><a class="css" data-link-type="property" href="#propdef-line-height-step" id="ref-for-propdef-line-height-step③">line-height-step</a>
      <td>&lt;length>
      <td>0px
      <td>block containers
      <td>yes
      <td>N/A
      <td>no
      <td>by computed value type
      <td>per grammar
      <td>absolute length
   </table>
  </div>
  <h2 class="no-num no-ref heading settled" id="issues-index"><span class="content">Issues Index</span><a class="self-link" href="#issues-index"></a></h2>
  <div style="counter-reset:issue">
   <div class="issue"> This proposal can be simplified down to just the <a class="property" data-link-type="propdesc" href="#propdef-block-step-size">block-step-size</a> property, represented solely through its shortened form as <a class="property" data-link-type="propdesc" href="#propdef-block-step">block-step</a>.
	This level will likely at most contain <span class="property">block-step-size</span> and <a class="property" data-link-type="propdesc" href="#propdef-block-step-insert">block-step-insert</a>, leaving <a class="property" data-link-type="propdesc" href="#propdef-block-step-align">block-step-align</a> and <a class="property" data-link-type="propdesc" href="#propdef-block-step-round">block-step-round</a> to be added if the future demands.
	The full design is described herein for current discussion and future reference.<a href="#issue-d3f7ebdb"> ↵ </a></div>
   <div class="issue"> This proposal is currently defined to apply only to block-level boxes. This limitation is solely to simplify the first iteration; it should eventually be extended to all layout modes that honor specified heights.<a href="#issue-906f23b3"> ↵ </a></div>
   <div class="issue">Should this be animatable?
	There doesn’t seem to be use cases but needed for consistency?<a href="#issue-27b8d19f"> ↵ </a></div>
  </div>
  <aside class="dfn-panel" data-for="propdef-block-step-size">
   <b><a href="#propdef-block-step-size">#propdef-block-step-size</a></b><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-propdef-block-step-size">2. Adjusting Block-level Box Heights</a> <a href="#ref-for-propdef-block-step-size①">(2)</a>
    <li><a href="#ref-for-propdef-block-step-size②">2.1. Specifying the Step Size: the block-step-size property</a>
    <li><a href="#ref-for-propdef-block-step-size③">2.2. Specifying the Spacing Type: the block-step-insert property</a> <a href="#ref-for-propdef-block-step-size④">(2)</a> <a href="#ref-for-propdef-block-step-size⑤">(3)</a>
    <li><a href="#ref-for-propdef-block-step-size⑥">2.3. Specifying Alignment: the block-step-align property</a> <a href="#ref-for-propdef-block-step-size⑦">(2)</a> <a href="#ref-for-propdef-block-step-size⑧">(3)</a> <a href="#ref-for-propdef-block-step-size⑨">(4)</a> <a href="#ref-for-propdef-block-step-size①⓪">(5)</a>
    <li><a href="#ref-for-propdef-block-step-size①①">2.4. Rounding Method: the block-step-round property</a> <a href="#ref-for-propdef-block-step-size①②">(2)</a> <a href="#ref-for-propdef-block-step-size①③">(3)</a> <a href="#ref-for-propdef-block-step-size①④">(4)</a>
    <li><a href="#ref-for-propdef-block-step-size①⑤">2.5. Block Step Adjustment Shorthand: the block-step shorthand</a> <a href="#ref-for-propdef-block-step-size①⑥">(2)</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="propdef-block-step-insert">
   <b><a href="#propdef-block-step-insert">#propdef-block-step-insert</a></b><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-propdef-block-step-insert">2. Adjusting Block-level Box Heights</a>
    <li><a href="#ref-for-propdef-block-step-insert①">2.2. Specifying the Spacing Type: the block-step-insert property</a>
    <li><a href="#ref-for-propdef-block-step-insert②">2.3. Specifying Alignment: the block-step-align property</a> <a href="#ref-for-propdef-block-step-insert③">(2)</a>
    <li><a href="#ref-for-propdef-block-step-insert④">2.5. Block Step Adjustment Shorthand: the block-step shorthand</a> <a href="#ref-for-propdef-block-step-insert⑤">(2)</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="valdef-block-step-insert-margin">
   <b><a href="#valdef-block-step-insert-margin">#valdef-block-step-insert-margin</a></b><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-valdef-block-step-insert-margin">2.3. Specifying Alignment: the block-step-align property</a> <a href="#ref-for-valdef-block-step-insert-margin①">(2)</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="propdef-block-step-align">
   <b><a href="#propdef-block-step-align">#propdef-block-step-align</a></b><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-propdef-block-step-align">2. Adjusting Block-level Box Heights</a>
    <li><a href="#ref-for-propdef-block-step-align①">2.3. Specifying Alignment: the block-step-align property</a> <a href="#ref-for-propdef-block-step-align②">(2)</a>
    <li><a href="#ref-for-propdef-block-step-align③">2.5. Block Step Adjustment Shorthand: the block-step shorthand</a> <a href="#ref-for-propdef-block-step-align④">(2)</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="valdef-block-step-align-center">
   <b><a href="#valdef-block-step-align-center">#valdef-block-step-align-center</a></b><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-valdef-block-step-align-center">2.3. Specifying Alignment: the block-step-align property</a> <a href="#ref-for-valdef-block-step-align-center①">(2)</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="valdef-block-step-align-start">
   <b><a href="#valdef-block-step-align-start">#valdef-block-step-align-start</a></b><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-valdef-block-step-align-start">2.3. Specifying Alignment: the block-step-align property</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="valdef-block-step-align-end">
   <b><a href="#valdef-block-step-align-end">#valdef-block-step-align-end</a></b><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-valdef-block-step-align-end">2.3. Specifying Alignment: the block-step-align property</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="propdef-block-step-round">
   <b><a href="#propdef-block-step-round">#propdef-block-step-round</a></b><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-propdef-block-step-round">2. Adjusting Block-level Box Heights</a>
    <li><a href="#ref-for-propdef-block-step-round①">2.1. Specifying the Step Size: the block-step-size property</a>
    <li><a href="#ref-for-propdef-block-step-round②">2.4. Rounding Method: the block-step-round property</a>
    <li><a href="#ref-for-propdef-block-step-round③">2.5. Block Step Adjustment Shorthand: the block-step shorthand</a> <a href="#ref-for-propdef-block-step-round④">(2)</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="valdef-block-step-align-up">
   <b><a href="#valdef-block-step-align-up">#valdef-block-step-align-up</a></b><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-valdef-block-step-align-up">2.4. Rounding Method: the block-step-round property</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="valdef-block-step-align-down">
   <b><a href="#valdef-block-step-align-down">#valdef-block-step-align-down</a></b><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-valdef-block-step-align-down">2.4. Rounding Method: the block-step-round property</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="propdef-block-step">
   <b><a href="#propdef-block-step">#propdef-block-step</a></b><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-propdef-block-step">1.1. East Asian Casual Vertical Rhythms</a> <a href="#ref-for-propdef-block-step①">(2)</a>
    <li><a href="#ref-for-propdef-block-step②">2. Adjusting Block-level Box Heights</a> <a href="#ref-for-propdef-block-step③">(2)</a>
    <li><a href="#ref-for-propdef-block-step④">2.5. Block Step Adjustment Shorthand: the block-step shorthand</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="propdef-line-height-step">
   <b><a href="#propdef-line-height-step">#propdef-line-height-step</a></b><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-propdef-line-height-step">1.1. East Asian Casual Vertical Rhythms</a> <a href="#ref-for-propdef-line-height-step①">(2)</a>
    <li><a href="#ref-for-propdef-line-height-step②">3. Adjusting Line Box Heights: the line-height-step property</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="step-unit">
   <b><a href="#step-unit">#step-unit</a></b><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-step-unit">2.1. Specifying the Step Size: the block-step-size property</a> <a href="#ref-for-step-unit①">(2)</a>
    <li><a href="#ref-for-step-unit②">3. Adjusting Line Box Heights: the line-height-step property</a> <a href="#ref-for-step-unit③">(2)</a> <a href="#ref-for-step-unit④">(3)</a> <a href="#ref-for-step-unit⑤">(4)</a> <a href="#ref-for-step-unit⑥">(5)</a> <a href="#ref-for-step-unit⑦">(6)</a> <a href="#ref-for-step-unit⑧">(7)</a> <a href="#ref-for-step-unit⑨">(8)</a> <a href="#ref-for-step-unit①⓪">(9)</a> <a href="#ref-for-step-unit①①">(10)</a> <a href="#ref-for-step-unit①②">(11)</a>
   </ul>
  </aside>
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